Heat exchanger for high power electrical component

ABSTRACT

A power electronics package includes a heat exchanger having a plurality of faces, a plurality of semiconductor devices mounted on the plurality of faces and at least one bus structure for interconnecting electrodes of the semiconductor devices. The package is enclosed by a cover and structure is provided to connect other electrodes of the semiconductor devices to an external circuit.

This is a divisional of U.S. application Ser. No. 07/764,238, filed Sep.23, 1991.

TECHNICAL FIELD

The present invention relates generally to electrical componentpackages, and more particularly to a package incorporating a heatexchanger for a high power electrical component.

BACKGROUND ART

There is a need, particularly in aircraft and aerospace installations,for compact and light weight power systems. Such power systems typicallyinclude a power converter that utilizes multiple highpower switcheshaving voltage and current ratings on the order of 1,000 volts and 1,000amps, respectively. Such power switches dissipate substantial amounts ofpower and thus develop heat which can adversely affect the performanceof the device and other electrical components in the vicinity thereof.The need to reduce system size and weight, however, greatly complicatesthe removal of heat.

Prior generating systems have utilized heat exchangers to whichsemiconductors or other high power handling components are mounted. Suchheat exchangers have been of the usual cooling fin type or have been ofthe type which utilize circulating cooling fluid. An example of thelatter type of heat exchanger is known as a jet impingement coolerdeveloped by the assignee of the instant application and which is shownin detail in Bland, et al., U.S. Pat. No. 4,494,171, the disclosure ofwhich is hereby incorporated by reference herein. Jet impingementcoolers are generally more efficient at heat removal than fin-type heatexchangers that rely upon movement of cooling fluid in a directionparallel to the faces of the fins.

Heidler, U.S. Pat. No. 3,070,729 discloses a modularized electricalnetwork assembly including a plurality of triangularly shaped miniaturecircuit subassemblies disposed about a heat exchanger and enclosed in ahousing. The heat exchanger includes fins separating the subassemblieswherein the fins provide means for circulating a cooling fluid adjacenteach of the subassemblies to remove heat developed thereby.

Sutrina, U.S. Pat. No. 4,614,964 discloses a semiconductor packagewherein a plurality of generally equally angularly spaced semiconductorsare located in a space between concentric power buses.

Patents disclosing stacked semiconductors with means carrying away heatdeveloped thereby include Grandia, U.S. Pat. No. 3,808,471, Bourbeau, etal., U.S. Pat. No. 4,010,489, Pollard, et al., U.S. Pat. No. 4,504,850,Lutfy, U.S. Pat. No. 4,559,580 (assigned to the assignee of the instantapplication), Parks, U.S. Pat. No. 4,841,355 and Carlson, U.S. Pat. No.4,862,249.

SUMMARY OF THE INVENTION

In accordance with the present invention, a heat exchanger is capable ofconducting large amounts of heat away from heat producing electricalcomponents.

More particularly, a heat exchanger includes a series of orifice platesstacked in an axial direction and separated from one another by spacerplates wherein the plates terminate at an outer flat wall portion andthe orifice plates include offset axial apertures therethrough wherebythe flat wall portion is adapted to receive a semiconductor device. Theheat exchanger is joined to a base and the base and heat exchanger havealigned axial channels therein for admittance of coolant whereby thermalconduction paths are established in a radial direction and whereby theorifice plates may be thermally linked by coolant flowing in the axialdirection thereby.

Preferably, the heat exchanger includes a distribution plenum and acollection plenum at opposite axial ends thereof.

In accordance with the preferred embodiment, a power bus is disposed onthe heat exchanger and is adapted to interconnect multiple electrodeleads of a semiconductor device. In accordance with a highly preferredform of the invention, the power bus includes a pair of arms coupled tothe multiple electrode leads of the semiconductor device. According toan alternative embodiment, the power bus includes a planar electricallyconductive portion coupled to the multiple electrode leads of thesemiconductor device.

According to a further aspect of the present invention, a cover ismounted on the base and encloses a heat exchanger, the power bus and thesemiconductor device. The cover may be electrically conductive andinclude an electrical connection tab thereon or may be electricallyinsulative, in which case an electrically conductive terminal is mountedin electrical contact with the base. In either case, the power busincludes an electrically conductive post in coaxial relationship withthe cover and extending through an aperture therein and a furtherconductive post is electrically connected to the control electrode ofthe transistor and extends through a further aperture of the cover.

In accordance with yet another aspect of the present invention, a powerelectronics module includes a heat exchanger having at least three outerfaces and at least three semiconductor devices mounted on the outerfaces wherein each semiconductor device includes first and secondelectrodes and wherein each first electrode is electrically connected bythe heat exchanger to the first electrodes of the remainingsemiconductor devices. Means are disposed in proximity to thesemiconductor devices for electrically connecting together the secondelectrodes thereof.

In accordance with still another aspect of the present invention, apower electronics module includes a cylindrical jet impingement coolerof polygonal shape in cross section having a plurality of outer facesabout a central axis and a plurality of transistors each disposed inthermal contact with a face of the cooler wherein each transistor hasfirst, second and third electrodes. Means are provided for enclosing thetransistors and the cooler and means are disposed in contact with theenclosing means for allowing connection of electrical conductors to theelectrodes of the transistors.

The present invention permits fabrication of a switch having very highvoltage and current ratings on the order of 1,000 volts and 1,000 amps,respectively, in a volume of less than 4 cubic inches in the preferredembodiment, using semiconductors to be placed in production in the nearfuture. As semiconductor chip sizes are further reduced in the future,the power-to-volume ratio of the package may be increased significantlyso that power generation system size and weight can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 comprises an exploded isometric view of a heat exchanger andpackage according to the present invention;

FIG. 2 comprises an isometric view, partly in section, of the assembledpackage of FIG. 1;

FIG. 3 comprises a sectional view of the heat exchanger taken along thelines 3--3 of FIG. 1;

FIG. 4 comprises a sectional view taken generally along the lines 4--4of FIG. 3;

FIG. 5 comprises a sectional view taken generally along the lines 5--5of FIG. 3;

FIG. 6 comprises an exploded isometric view similar to FIG. 1illustrating an alternative embodiment of the present invention; and

FIG. 7 comprises an exploded isometric view similar to FIGS. 1 and 6illustrating a still further alternative embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a package 10 for a high power electricalcomponent includes a base 12 fabricated of an electrically and thermallyconductive material. The base 12 may include an oversized flange 14having one or more holes 16 therein for mounting of the package to acircuit board or other substrate.

Disposed on the base 12 is a heat exchanger 18 in the form of a jetimpringement cooler which is right cylindrical and polygonal in crosssection and includes a series of outer planar faces 20 disposed indiffering planes. In the preferred embodiment, there are six faces 20,and hence the heat exchanger is hexagonal in cross section. Also, in thepreferred embodiment, the heat exchanger 18 is electrically conductiveand, as seen in FIGS. 3-5, includes a series of orifice plates 21stacked in an axial direction and separated from one another by spacerplates 22.

As seen specifically in FIGS. 3 and 4, the orifice plates 21 includeoffset apertures 23 therethrough. Each orifice plate 21 includes acentral bore 24 which, when the orifice plates 21 are stacked with thespacer plates 22, is aligned with a central tube section 25 carried bythe spacer plate 22 to form an axial channel 26. The axial channel 26 isaligned with an axial channel 27 extending through the base 12. The heatexchanger 18 further includes a distribution plenum 28 enclosed in partby a cover plate 29 at a first axial end thereof and a collection plenum30 at an opposite axial end thereof. The collection plenum 30 is influid communication with a fluid channel 31 disposed in the base 12. Thebase 12 further includes first and second annular channels 32, 33 thataccommodate fluid seals (not shown) which prevent leakage of coolant outof the channels 27, 31, respectively, when the base 12 is mounted on asubstrate.

If desired, the spacer plates 22 may be modified to omit the centraltube sections 25, in which case a separate tube (not shown) extendsthrough the aligned central bores 24 in the orifice plates 21 to directcoolant into the distribution plenum 28.

During operation of the heat exchanger 18, coolant is supplied throughthe aligned channels 26, 27 and is distributed to the plates 21, 22through the distribution plenum 28. Heat conduction paths areestablished through the orifice plates 21 in a radial direction and theorifice plates 21 are thermally linked by coolant flowing in the axialdirection therebetween. The offset apertures 23 ensure that coolant isdirected against the heat conduction paths perpendicular to the radialheat conduction paths so that cooling efficiency is established at ahigh level.

Mounted on one or more faces 20 of the heat exchanger 18 are high powerelectrical components in the form of insulated gate bipolar transistors(IGBT's) 34 that are generally planar in shape wherein each includes acontrol electrode and main current path electrodes. More specifically,the IGBT's 34 include one or more gate bonding sites 35 and one or moreemitter bonding sites 36. In addition, each IGBT 34 includes a Collectorelectrode 37 on a rear face of the IGBT 34. The IGBT's 34 are solderedor otherwise joined directly to the faces 20, or are soldered orotherwise secured to an intermediate electrically and thermallyconductive plate (not shown) having a low coefficient of thermalexpansion which is in turn electrically and thermally secured to theface 20. In either event, the collectors 37 of the IGBT 34 areelectrically interconnected by the heat exchanger 18 and a path for heattransfer is established from the IGBT 34 to the coolant flowing in theheat exchanger 18.

Disposed atop an upper face 38 of the heat exchanger 18 is a sheet ofelectrical insulation 39, which may be made of a material known asNomex, a registered trademark of E. I. Du Pont de Nemours and Companyfor flexible film for electrical insulation.

An electrically conductive plate comprising a gate bus 40 is disposedatop the sheet of electrical 10 insulation 39. The gate bus 40 is thuselectrically isolated from the heat exchanger 18 and includes bondingtabs 41 which are soldered or otherwise electrically connected to theupper gate bonding sites 35 of the IGBT's 34. The gate bus 40 furtherincludes an upwardly extending terminal 43 which is offset from acentral axis 44 of the heat exchanger 18.

A further electrical insulator 45 is disposed atop the gate bus 40 suchthat the terminal 43 extends through an aperture 47 therein. Theelectrical insulator 45, which may be fabricated of plastic (forexample, a thermoplastic fabricated of polyetheretherketone), includes amain body 48 and a plurality of downwardly depending arms 49 which aredisposed over and cover corners 51 of the heat exchanger 18 at whichadjacent faces 20 meet. An electrically conductive emitter power bus 53is disposed atop the electrical insulator 45, in the preferredembodiment, includes a plurality of arms 55 which are disposed over themain body 48 and the arms 49 of the electrical insulator 45. Thedownwardly depending portions of the arms 55 are thus electricallyisolated from the heat exchanger 18 by the arms 49 and the emitter bus53 is further electrically isolated from the gate bus 40 by the mainbody 48 of the electrical insulator 45.

The sheet of electrical insulation 39, the gate bus 40, the electricalinsulator 45 and the emitter bus 53 are maintained in place atop theheat exchanger 18 by adhesive and fasteners, as required.

As seen in FIG. 2, wire bonds 57 are attached between the emitterbonding sites 36 of the IGBT's 34 and an adjacent leg 55 of the emitterbus 53. As should be evident from the foregoing discussion, the sixIGBT's 34 are thus electrically connected in parallel with the gates ofthe IGBT's 34 connected together by the gate bus 40, the emittersconnected together by the emitter bus 53 and the collectors connectedtogether by the heat exchanger 18.

The emitter bus 53 further includes an upwardly extending post 59 which,when assembled on the heat exchanger 18 and intervening components,includes a central axis 60 coincident with the central axis 44 of theheat exchanger 18. A cover assembly 63 includes a right circularcylindrical, electrically conductive main body 65 which, in thepreferred embodiment, is cold welded or otherwise joined to the base 12and is thus electrically connected thereto. An electrically conductiveconnection terminal in the form of a tab 67 is soldered or otherwiseelectrically and mechanically joined to the main body 65. Inasmuch asthe collectors of the IGBT's 34 are electrically connected to the heatexchanger 18 and the base 12, and since the base 12 is electricallyconnected to the cover 65, it follows that a path for collector currentsmay be established to other components through the connection tab 67.

The cover assembly 63 further includes an electrically insulativewasher-shaped top plate 69 fabricated of ceramic, glass or anotherelectrically insulating material. Carried by the top plate 69 is anelectrically conductive base connection post 71 and an electricallyconductive emitter connection post 73, both of which are electricallyisolated from each other and from the main body 65 and the connectiontab 67. The posts 71, 73 are crimped or otherwise electrically connectedto the terminal 43 and the post 59, respectively. In addition, the post71 is coincident with the central axis 44 of the heat exchanger 18 whilethe base connection post 71 is offset relative thereto. Since thecollector and emitter currents are conducted through concentricconductors, and since current flow occurs in opposite directions in thebody 65 and the post 73, cancellation of magnetic fields arising fromsuch current flow is accomplished.

Further, the particular arrangement of the connection tab 67 and theconnection post 73 is such as to facilitate utilization of laminatedflat bus work in circuitry external of the package 10, again allowingcancellation of magnetic fields and greatly reducing parasiticinductance losses.

It should be noted that while the illustrated embodiment shows sixIGBT's connected in parallel within a single package, the package mayalternatively contain a different number of IGBT's connected in parallelor connected in a different circuit configuration. In such a case,emitter and gate buses of different design would be used to interconnectIGBT electrodes as required. Thus, for example, a full inverter phasecan be constructed wherein three IGBT's are connected in parallel andcomprise an upper inverter phase switch and the remaining three IGBT'sare also connected in parallel and comprise a lower inverter phaseswitch. In this case, the emitter and base buses must each be dividedinto two separate buses each having a terminal or post for connectionthereto.

FIG. 6 illustrates an alternative embodiment of the present inventionwherein the hermetic construction of FIGS. 1-5 is replaced by anonhermetic package. Elements common to FIGS. 1 and 6 are assigned thesame reference numerals. In the embodiment of FIG. 6, the electricallyconductive cover 63 is replaced by an electrically nonconductive cover80 fabricated of an electrically insulative material, such as plastic.Carried by the cover 80 are the base connection post 71 and the emitterconnection post 73. The connection tab 67 is not carried by the cover80; rather, the tab 67 is soldered or otherwise electrically connectedto and carried by the base 12. The cover 80 is secured by adhesive orany other suitable means to the base 12 such that it encloses the heatexchanger 18, the IGBT's 34 and the remaining components of the package.

FIG. 7 illustrates a still further embodiment of the present invention.Again, elements common to FIGS. 1 and 7 are assigned like referencenumerals. In the embodiment of FIG. 7, the IGBT's 34 are replaced byhermetically sealed transistor packages 90. Each package 90 includes anelectrically conductive mounting plate 92 that is coupled to a firstmain current path electrode of the transistor 90 and a series ofelectrode conductors 94a-94e. The electrode conductors 94a, 94b areconnected to a second main current electrode of the transistor 90. Theelectrode conductors 94c, 94d comprise Kelvin connections for the IGBT90 while the electrode conductor 94e is coupled to the control or gateelectrode of the IGBT 90. The IGBT 90 comprises a TO220 or TO258semiconductor device, although it may comprise a different device, ifdesired. The electrode plate 92 of each IGBT 90 is soldered to a face 20of the heat exchanger 18 such that the electrode conductors 94a-94eextend upwardly away from the base 12 above the upper face 38 thereof. Apower bus 100 includes a series of via holes 102 through which theelectrode conductors 94a-94e extend. The power bus 100 may comprise amulti-layer circuit board having conductive traces and pathways andpathways which serve to connect the electrode conductors 94a, 94b of thedevices 90 together to an electrically conductive terminal post 104centrally mounted on the bus 100. In like fashion, conductive traces andpathways interconnect the electrodes 94e of the transistors 90 togetherto an electrically conductive connection post 106 mounted on the bus100. If necessary or desirable, further electrically conductive postsmay be mounted on the bus 100 and conductive traces may be supplied tointerconnect the electrode conductors 94c and the electrode conductors94d to such posts. As before, the first main current path electrodes ofthe transistors 90 are interconnected by the heat exchanger 18.

As with the embodiment of FIGS. 1-5, the cover assembly 63 is placedover the assembled component and is cold welded or otherwise joined tothe base 12. As before, the posts 71, 73 are crimped or otherwiseelectrically connected to the posts 104, 106.

Alternatively, the cover 80 of FIG. 6 may be secured by adhesive orother means to the base 12. In that event, the connection tab 67 iselectrically mounted on the base 12, as before.

While the embodiment of FIG. 7 results in a larger package for a givenpower rating than the embodiments of FIGS. 1-6, this disadvantage is atleast partially offset by the simplified construction of the package.

In each of the foregoing embodiments, the heat exchanger 18 iselectrically connected directly to the base 12. If necessary ordesirable, the heat exchanger 18 may be electrically isolated from thebase 12 by means of an insulating substrate and a further terminal maybe connected to the heat exchanger 18 to permit connection to thecollectors of the IGBT's, if desired.

Numerous modifications and alternative embodiments of the invention willbe apparent to those skilled in the art in view of the foregoingdescription. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the best mode of carrying out the invention. The details of thestructure may be varied substantially without departing from the spiritof the invention, and the exclusive use of all modifications which comewith the scope of the appended claims is reserved.

I claim:
 1. A heat exchanger comprising:a series of orifice platesstacked in an axial direction and separated from one another by spacerplates, the plates all terminating at an outer flat wall portion and theorifice plates having offset axial apertures therethrough, the flat wallbeing adapted to receive a heat source; and a base to which the heatexchanger is joined; wherein the base and heat exchanger have alignedaxial channels therein for admittance of coolant whereby thermalconduction paths are established in a radial direction and wherein theorifice plates may be thermally linked by coolant flowing in the axialdirection therebetween; and a heat source mounted on said outer flatwall portion.
 2. The heat exchanger of claim 1, further including adistribution plenum and a collection plenum at opposite axial endsthereof.
 3. The heat exchanger of claim 1 wherein said heat exchangerdefines a single fluid circuit therein for passage therethrough of saidcoolant; and said heat source is thermally linked to said coolant bythermal conduction through said wall.